In the intaglio printing (gravure, for short), screen dots are concave relative to a surface of the plate. When printing, the printing ink is filled in the concave screen dots and is transferred to medium by imprinting.
Due to the above features of the intaglio printing, there is a space similar to a wall between screen dots, i.e., “screen wall”. Concave screen dots are formed on the plate regardless of whether the platemaking the intaglio printing is finished in a manner of manual corrosion or in a manner of electrographic engraving. Therefore, change rules of the “screen wall” are very important, in particular, in dark areas.
The inventors found that the pattern of the “screen wall” and the change rule of the “screen wall” in the dark areas directly influence gradation quality and texture of the dark portions during the intaglio printing. During the intaglio printing, the “screen wall” becomes thinner relatively as the gradation becomes darker, i.e., the screen dots become larger. However, the “screen wall” becomes thinner, and thus it will make the “screen wall” to fracture or have non-uniform thickness or the like, which will cause problems, for example the dark area will present texture or “water ripple”. That is, in the conventional art, the pattern of intaglio printing screen dot (i.e., screen pattern) is square and the pattern of “screen wall” is normal rectangle, but the “screen wall” will change as amplitude modulation screening points change due to the gradation changes. The screen pattern in the change process is similar to rectangle but is not rectangle, the thickness of the rectangle is non-uniform, which will cause texture or “water ripple”.